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J Cereb Blood Flow Metab. 2019 Apr 5:271678X19839502. doi: 10.1177/0271678X19839502. [Epub ahead of print]

Characterizing white matter fiber orientation effects on multi-parametric quantitative BOLD assessment of oxygen extraction fraction.

Author information

1
1 Department of Diagnostic and Interventional Neuroradiology, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.
2
2 TUM Neuroimaging Center (TUM-NIC), Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.
3
3 Departments of Radiology & Biomedical Imaging and of Biomedical Engineering, Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.
4
4 Department of Diagnostic and Interventional Radiology, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.
5
5 Clinic for Neurology, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.

Abstract

Relative oxygen extraction fraction (rOEF) is a fundamental indicator of cerebral metabolic function. An easily applicable method for magnetic resonance imaging (MRI) based rOEF mapping is the multi-parametric quantitative blood oxygenation level dependent (mq-BOLD) approach with separate acquisitions of transverse relaxation times T2* and T2 and dynamic susceptibility contrast (DSC) based relative cerebral blood volume (rCBV). Given that transverse relaxation and rCBV in white matter (WM) strongly depend on nerve fiber orientation, mq-BOLD derived rOEF is expected to be affected as well. To investigate fiber orientation related rOEF artefacts, we present a methodological study characterizing anisotropy effects of WM as measured by diffusion tensor imaging (DTI) on mq-BOLD in 30 healthy volunteers. Using a 3T clinical MRI-scanner, we performed a comprehensive correlation of all parameters ( T2* , T2, R2' , rCBV, rOEF, where R2' =1/ T2* -1/T2) with DTI-derived fiber orientation towards the main magnetic field (B0). Our results confirm strong dependencies of transverse relaxation and rCBV on the nerve fiber orientation towards B0, with anisotropy-driven variations up to 37%. Comparably weak orientation-dependent variations of mq-BOLD derived rOEF (3.8%) demonstrate partially counteracting influences of R2' and rCBV effects, possibly suggesting applicability of rOEF as an oxygenation sensitive biomarker. However, unresolved issues warrant caution when applying mq-BOLD to WM.

KEYWORDS:

Anisotropy; diffusion tensor imaging; multi-parametric quantitative BOLD; oxygen extraction fraction; white matter

PMID:
30952200
DOI:
10.1177/0271678X19839502

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